The present invention relates to a color video printer for printing a color television picture and a color masking circuit for use in a color video printer or the like, and particularly relates to a color masking circuit which performs high-speed color masking processing to eliminate color impurities included in the color material and the like so as to obtain a printed picture with high color reproducibility.
A color video printer for fixing and recording a color television picture as a hard copy has become widely used in various fields as an alternative to photography or some other printing technique. There are various color video printers available which utilize different recording systems such as thermal transfer, ink-jets, light-spot scanning, etc. In any recording system, however, color reproduction is achieved by mixing the three colors of yellow (Y), magenta (M) and cyan (C) using a subtractive color process.
In thermal transfer printing of a sheet of printed matter, it is easy to obtain a superimposed color picture by switching color ink ribbons of the colors (Y), (M) and (C). Recently, therefore, a full-color video printer in which density gradation is given to respective picture elements (recording dots) has been developed and is expected to be used as an external output apparatus (a hard-copy device) to be connected to a video receiver, a picture processing device, a personal computer and so on. In controlling the density gradation, a constant voltage is applied to each of the heating resistors of a thermal head and current conduction time to the resistors is controlled to thereby cause the heating energy of the resistors to be different so as to give gradation to the transfer quantity of a color material (ink) to recording dots, that is, to give density gradation to picture elements.
In the conventional color video printer, however, the color reproducibility of printed pictures has not been superior. This is mainly because the colors (Y, M and C) of general color materials are not pure but include impurities. Therefore, if those primary colors are superimposed on a printed paper, the mixed color thereon shifts from the color of the original picture.